Children who get chickenpox may be at increased risk for
stroke soon after the infection, a new study from the United Kingdom suggests.

The study analyzed information from 49 children who were
followed for about 6.5 years, and who experienced both chickenpox and stroke at
some point during the study period.

Children were four times as likely to have a stroke during
the six months following infection with chickenpox, compared with their risk at
other time points during the study.

However, stroke in children is rare — about 6 out of 100,000
children under 15 have a stroke each year, according to the National Stroke
Association. That means that the risk that any given child will experience a
stroke after chickenpox is quite small.

Still, the findings add to a growing body of research
linking chickenpox with stroke. A 2001 study found that about 31 percent of
children who had a stroke had chickenpox in the previous year, compared with 9
percent of all children had the infection in the last year. [7 Devastating
Infectious Diseases]

Among children who do experience stroke, complications such
as neurological problems are common, said the researchers from the London
School of Hygiene and Tropical Medicine. More studies should be conducted to
determine how chickenpox and other infections might increase the risk of stroke
in children in order to identify strategies to prevent the condition, the
researchers said.

The researchers gathered information from electronic health
care records of millions of adults and children in the United Kingdom. No link
between chickenpox and stroke was found for adults.

Because the study included only children who had experienced
both stroke and chickenpox, it eliminated problems that might arise by trying
to compare children who did and did not get chickenpox (who might have
different underlying risk factors), the researchers said. Still, the study
found an association, and cannot prove that chickenpox can cause stroke.

Heart problems (caused by birth defects), and conditions
such as sickle cell disease and trauma to the arteries are known causes of
stroke in children, according to the American Heart Association.

It's possible that the chickenpox virus damages or inflames
the arteries, increasing the risk of a blocked artery that would lead to a
stroke. The chickenpox virus can replicate in the artery walls in the brain,
the researcher said.

"The study illustrates that immunization against
varicella is important to reduce the risk of complications" from chickenpox,
although they are rare, said Dr. Warren Lo, a neurologist at Nationwide
Children's Hospital in Columbus, Ohio, who was not involved in the study.

Because of vaccination in the United States, chickenpox is
not very common among kids in this country, said Dr. Otto Ramos, director of
the Pediatric Infectious Disease Division at Miami Children's Hospital. (The
chickenpox vaccine is not routinely given to children in the United Kingdom.)

A study published last year found that cases of chickenpox
in the United States declined nearly 80 percent in the last decade, after
introduction of the vaccine in 1996.

But cases do still occur, and Ramos said he will now be more
inclined to look for a history of chickenpox or other infections in children
who have had strokes and do not have other risk factors for the condition.